As a background art in this technical field, there are disclosed in JP-A-2000-195453 (PTL 1) and JP-T-2005-521990 (PTL 2). In a charged particle beam device represented by a scanning electron microscope or a transmission electron microscope, the charged particle beam focused thinly by an electrostatic lens, an electromagnetic lens, or the like is scanned on the sample, and desired information (for example, the sample image) is obtained from the sample.
In such a charged particle beam device, in a case where the trajectory of the charged particle beam is deviated from the central axis of the objective lens (in a case where the optical-axis deviation occurs), the transverse chromatic aberration of the lens is increased. The increase of the aberration causes the resolving power or the resolution of the sample image to decrease remarkably. In addition, the optical-axis deviation causes the reduction of the brightness of the sample image, or the deviation of a field of view during the focus adjustment.
In a case where the thermionic-emission electron gun represented by the tungsten filament is used as a charged particle source, the filament is cut in several tens to several hundreds of hours. In a case where the filament is cut, the replacing work of the filament is necessary. The position of the charged particle source is changed before and after the replacement of the filament, and thus the axial adjustment for correcting the position change is required. The position of the charged particle source affects particularly on the brightness when the sample image is acquired.
The axial adjustment according to the replacing work and the replacement is required similarly, for example, even in a case where a field emission type electron gun is used other than the tungsten filament.
Accordingly, in order to acquire the sample image without the deviation of the field of view with high resolution and high brightness, the optical axis of the charged particle beam device is necessarily adjusted with high accuracy.
As a conventional axial adjustment method, a method is known which manually adjusts operating conditions of a deflector (aligner) for axial adjustment such that the movement of the sample image and the like caused by the change of the excitation current when the excitation current of the objective lens and the like are changed periodically.
In JP-A-2000-195453 (PTL 1), a technique is disclosed which automatically adjusts the optical axis of the charged particle beam by changing the excitation setting value of the aligner on the basis of the transition of the electron beam irradiation position which is changed between two excitation conditions of the objective lens.
In JP-T-2005-521990 (PTL 2), a technique is disclosed which electromagnetically and automatically adjusts the virtual position of the charged particle source or the like such that a gun alignment coil provided in the lower level of the charged particle source improves the brightness of the sample image.